PICLAB: CHEMICAL EQUILIBRIUM
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Chemical reactions that can occur in either direction
REVERSIBLE REACTIONS
reversible reactions
– Most reversible reactions do not go to completion. - That is, even when reactants are mixed, they are not completely converted to products.
aA+bB =cC+dD
REVERSIBLE REACTIONS – where • the capital letters represent formulas • the lowercase letters represent the stoichiometric coefficients in the balanced equation. – Double arrow: reaction is reversible • Both the forward and reverse reactions occur simultaneously.
Main idea of Chemical Equilibrium
Chemical equilibrium exists when two opposing reactions occur simultaneously at the same rate.
Disturbing a system at Equilibrium: Predictions: Once a reacting system has reached equilibrium, it remains at equilibrium until it is disturbed by some change of conditions.
LE CHATELIER’S PRINCIPLE
CONDITIONS (stress) Three types of changes can disturb the equilibrium of a reaction.
• Changes in concentration • Changes in pressure or volume (for reactions that involve gases) • Changes in temperature
If a system at equilibrium is disturbed by changing its conditions (applying a stress), the system shifts in the direction that reduces the stress.
LE CHATELIER’S PRINCIPLE
When the reaction shift to the RIGHT, it favors the _______ reaction.
FORWARD
When the reaction shift to the RIGHT, it favors the forward reaction. Therefore, ____ products are formed.
MORE
When the reaction shift to the LEFT, it favors the _______ reaction.
REVERSE
When the reaction shift to the LEFT, it favors the Reverse reaction. Therefore, ____ products are formed.
LESS
Releases Heat, ∆ (Assume heat as product)
EXOTHERMIC REACTION
Absorbs Heat, ∆ (Assume heat as reactant)
ENDOTHERMIC
Changes in pressure have little effect on the concentrations of solids or liquids because they are only slightly compressible.
CHANGE IN PRESSURE AND VOLUME
changes in pressure do cause significant changes in concentrations of gases.
CHANGE IN PRESSURE AND VOLUME
– Shift to the Right (favors forward reaction)
PRESSURE INCREASE ( Volume Decrease)
– Shift to the Left (favors reverse reaction)
PRESSURE DECREASE (Volume Increase)
• Adding a catalyst to a system changes the rate of the reaction (speeds up) • But this does not shift (affect) the equilibrium in favor of either products or reactants.
ADDITION OF CATALYST